Disordered plane waves in the transition between target and antitarget patterns

Since the experimental observation of antiwaves in reaction-diffusion (RD) systems, the discrepancy between the theoretical prediction and the experimental observation on the transition from inwardly rotating chemical waves to normal waves remains an unsolved problem. Theoretical predictions using both RD model and complex Ginzberg-Landau equation indicate that there exists a trend in which wave vector approaches to zero in the transition process, while disordered plane waves near the onset were observed in experiment. This discrepancy motivated us to conduct a systematic research to investigate the transition. Using chlorite-iodide-malonic acid reaction as model system and with a thorough parameter scanning, we found clear trend that the wave vector decreased near the transition point, where wavelength diverged. This observation is consistent with the theoretical predictions. However, disordered plane waves appeared in the region near the onset. Comparing the experimental results with the results from numerical simulation, we found that spatial inhomogeneity of the diffusion coefficient was the main cause of the disordered plane waves.